Format using rustfmt-nightly

[jameshurst]

rustfmt has split in to rustfmt and rustfmt-nightly, the latter of which only compiles on the nightly toolchain. The nightly version of rustfmt is the one that is actively developed and seems to enforce a better style.

[tafia]

Isn't it slightly problematic to require a tool that can change everyday? I mean for every single pull request you must update rustfmt. That looks overkill to me.

[jameshurst]

I agree that reinstalling rustfmt for every build is kind of overkill. What the travis script currently does actually runs it for a third of the builds than it did previously since it only runs on the nightly toolchain.

Another option here would be to not run rustfmt in the travis script seeing how much rustfmt is currently changing.

[tafia]

I would if possible use a stable version of rustfmt. Not sure it exists.

[frewsxcv]

My thoughts:

• style changes are cool, whatever works
• i'm alright with having CI check enforce style
• rustfmt-nightly does seem to be changing style somewhat regularly from what i've seen

I'm alright with merging as is, and if it becomes too much of a burden in subsequent PRs, we can disable it.

[jameshurst]

@tafia we previously did use the stable version but that version is no longer being worked on and any new changes to rustfmt are going in to rustfmt-nightly. Even when we were using the stable version we were reinstalling rustfmt for every CI build anyways since cargo doesn't provide a way to update a binary if required.

[frewsxcv]

Relevant article: http://www.ncameron.org/blog/rustfmt-changes/

[tafia]

Thanks for the article, I haven't seen it. I guess if you are both ok then we can go for it. I'm just a little worried but we can at least give it a try.

[frewsxcv]

Yep, I have hesitations too, but I think it's okay to try out for a little while. Who knows, maybe we'll find some bugs we can report upstream and help out the community :)

Thanks for the PR @jameshurst